The present invention relates generally to a method and apparatus for detecting damage in plant products and, more particularly, to a method and apparatus for citrus fruit decay detection using substantially a single wavelength of light and sorting the plant products by damage categories.
In the plant product processing industry, a quantity of plant products are often stored and/or shipped together while packed into an enclosed space. If one or more of the packed plant products is damaged by even a small amount of decay, the close packing often allows that decay to spread quickly to other plant products. In addition, pre- or post-harvesting mechanical damage to the plant products, such as punctures or cuts, may allow decay to afflict the plant products more quickly than if the outer surface of the plant products were whole and undamaged. Since decayed plant products are unhealthy and unattractive to the consumer, government regulations require a minimal amount of decay in plant products provided for human consumption. Decay can be very expensive for producers of plant products since entire shipments of plant products may be refused by the retailer or consumer due to the presence of decay above the government-mandated levels.
It is critically important for processors and packagers of plant products to detect, and even distinguish among, decay, pre-harvest mechanical damage, post-harvest mechanical damage, blemishes, stems, blossoms, firmness, or water content (hereafter referenced generally as “damage”) to the plant products before those products are packaged for shipping, at least partially so that a small spot of decay on one plant product does not allow decay to spread throughout the shipment. Traditionally, damage inspections were done by trained human inspectors. However, even the most conscientious inspector has moments of inattention and the inspector's visual acuity can be dulled by long hours of repetitive and uninteresting inspection work. Moreover, damage can be extremely difficult for a human inspector to see because of inefficient viewing angles, extremely small areas/amounts of damage, or damage that is a similar color to the natural color of the plant product.
Many different schemes have been proposed for detecting damage or foreign matter in plant products. For example, U.S. Pat. No. 3,930,994, issued Jan. 6, 1976 to Conway et al., discloses a system which uses infrared light to penetrate a plant product and thereby produce an assessment of internal damage. However, due to natural variations in size, shape, and density of plant products of even the same species, the transmittal of light through the plant product is not uniform enough to provide reliable results and any such inspection system must discard many “good” plant products to be sure of eliminating a large percentage of “bad” plant products.
An alternate scheme and device is presented in U.S. Pat. No. 5,487,472, issued Jan. 30, 1996 to Satake et al. (hereafter referenced as '472). The '472 device uses reflected light to detect damage to the outer surface of a plant product. The reflected light is of multiple wavelengths specially chosen to highlight damage to the plant product. Unfortunately, the use of a spectrum or multiple wavelengths adds greatly to the cost, size, and complexity of this type of inspection system and also increases the chances of an acceptable blossom, stem, or natural blemish on the plant product causing a false positive damage scan and resultant waste of good plant products. Additionally, the '472 device does not provide a thorough inspection of substantially the entire surface of the plant product because the plant product passes through the inspection system while lying on a conveyor belt, so the belt blocks part of the plant product from view.
The present invention is directed to overcoming one or more of the problems as set forth above.